1. Technical Field of the Invention
The present invention relates to a method and an apparatus for managing a charge/discharge current of a battery loaded, for example, on a passenger car and a truck, and more particularly, to the managing apparatus in order to control an on-vehicle generator in consideration of an offset of the charge/discharge current
2. Related Art
Measurement of charge/discharge current of a battery loaded on a vehicle (hereinafter referred to just as a “battery”) enables control of electric power generation conditions of a generator loaded on the vehicle (hereinafter referred to just as a “generator”) so as not to cause overdischarge or overcharge of the battery. A measurement value derived from a current sensor after measurement of a charge/discharge current of a battery generally includes an error due to offset of the current (i.e., an offset error).
For coping with such an offset error, Japanese Patent Application Laid-Open No. 2005-100682, for example, discloses a battery charge/discharge current measuring apparatus which is able to determine the offset error. This battery charge/discharge current measuring apparatus controls the amount of power generation of the generator so that a measurement value derived from the current sensor may substantially become zero. Then, the voltage variation of the battery after lapse of a predetermined period T is measured. When the amount of variation of the battery voltage is within a predetermined range, the measurement value derived from the current sensor after lapse of the predetermined period T is determined as being an offset error D (i.e., an amount of offset of the charge/discharge current).
The technique disclosed in Japanese Patent Application Laid-Open No. 2005-100682, however, has suffered from the following drawbacks in observing a zero level of the current measured by the current sensor:
(1) In making a zero-level determination by a control unit which is located apart from the current sensor, an output signal of the current sensor is superposed by the ignition noise, because the battery is generally located in an engine room, thus disabling stable measurement of the current.
(2) The generated voltage of the generator is controlled to make a determination of an offset error based on the zero-level battery voltage variation. However, where the output current is varied caused by variations in the number of revolutions and the excitation current of the generator, the variation in the output current may be erroneously determined as being the error of the current sensor.
(3) Blind determination of the offset error under the unstable measuring conditions may make the offset error indefinite, which in turn may disturb the capacity control based on current integration.